Novel composite

ABSTRACT

THIS INVENTION RELATES TO NEW PROCESSES AND TO A NOVEL CORROSION RESISTANT BRIGHT DECORATIVE CHROMIUM COMPOSITE METAL COATED ARTICLE COMPRISING: (1) A FIRST LAYER OF COPPER; (2) A SECOND THIN LAYER OF BRIGHT COBALT THEREON; (3) A THIRD THIN LAYER CONTAINING NICKEL HAVING A THICKNESS OF 2-12 MICRONS; AND (4) A FOURTH LAYER OF BRIGHT DECORATIVE CHROMIUM ON SAID THIRD NICKEL-CONTAINING LAYER TO FORM AN ARTICLE BEARING A CORROSION RESISTANT BRIGHT DECORATIVE CHROMIUM SURFACE.

United States Patent Ofice 3,679,381 Patented July 25, 1972 ABSTRACT OF THE DISCLOSURE This invention relates to new processes and to a novel corrosion'resistant bright decorative chromium composite metal coated article comprising:

(1) a first layer of copper;

(2) a second thin layer of bright cobalt thereon;

(3) a third thin layer containing nickel having a thickness of 2-12 microns; and

(4) a fourth layer of bright decorative chromium on said third nickel-containing layer to form an article bearing a corrosion resistant bright decorative chromium surface.

This invention relates to novel metal composites having improved corrosion resistance and to methods and compositions for preparing such metal composites.

It is known that combinations of metal electroplates may be employed to form metal laminates having varying degrees of resistance to corrosion, ductility, brightness, and smoothness. Triple layer systems, for example, using a different nickel-containing deposit for each layer are known in the art wherein the amount of sulfur in each deposit is varied in order to control the relative potentials of the deposits. Chromium electrodeposits have been used over nickel and nickel-alloy electrodeposits in combination with copper or nickel undercoating and a coppernickel alloy deposit. The prior art processes and composite coatings are known to require relatively thick individual layers of metal in the composite, or if one layer is reduced in thickness, it may be necessary to provide a thicker layer of another section of the composite. In addition, composite electrodeposits which may be outstanding in one particular physical or chemical property such as superior brightness or resistance to electrochemical etching, may be found to be deficient in other desirable properties such as corrosion resistance, ductility, or lack of uniformity due to the complexity of the plating processes employed to prepare the metal composite.

It is an object of this invention to provide a novel bright decorative chromium composite metal plate characterized by its ability to provide improved corrosion resistance under adverse physical and chemical conditions. Another object of the invention is to provide a novel bright decorative chromium composite metal plate using an extremely thin layer of cobalt as part of the deposit. Other objects of the invention will be apparent to those skilled in the art from inspection of the following detailed description of the invention.

It has now been found that unexpectedly improved corrosion-resistant bright decorative chromium composite metal coatings may be prepared by depositing a first layer of copper, a second thin layer of bright cobalt thereon, a third thin nickel deposit, and a fourth layer of bright decorative chromium on said third nickel deposit using the bath compositions of the invention herein.

In accordance with certain of its aspects, the novel process of this invention for preparing a corrosion resistant bright decorative chromium composite metal plate comprises:

1 (1) Depositing on a basis metal a first layer of copper p ate;

(2) Depositing on said copper plate a second thin layer of bright cobalt;

(3) Depositing on said layer of cobalt a third thin layer corditaining nickel having a thickness of 20-120 microns; an

(4) Electrodepositing on said third nickel-containing layer a fourth layer of bright decorative chromium.

The basis material which may be plated in accordance with the invention herein to produce a novel corrosion resistant bright decorative chromium composite metal surface thereon may include iron alloys such as steel;

copper; nickel; brass; bronze; zinc; or alloys of any of these metals; plastics such as (ABS) acrylonitrile-butadrone-styrene, polypropylene, polyethylene, polystyrene, polyacrylates; etc. Exceptionally good results are obtained when the basis metal is steel or a zinc-base die-casting or when the basis material is ABS.

The first step of the process of this invention comprises deposition onto the basis material of a deposit of copper hereinafter referred to as the first (or base) layer. Deposition onto the zinc-base die-casting or other basis metal of the desired first layer of copper plate may be effected by depositing copper, for example, from a cyanide-copper plating bath, a pyrophosphate copper plating bath, or an acid-copper plating bath. Typically such baths may have the compositions set forth in Table I wherein all values are in grams per liter (g./l.) except where otherwise indicated:

In addition, bath composition (B) may contain a heterocyclic urea in amounts of from 0.5-10.0 g./l. (preferably 0.7-4.0 mg./1.) in combination with a carrier polyether in effective amounts of 0005-10 g./l. (preferably 0.1-1.0 g./l.) and a polysulfide of the formula such as f N o C 8 3S( H3]3 S S \CHz/a 503N8- in effective amounts of 0.001 g./l.-1.0 g./l. (preferably 0.005 g./l.-0.2 g./l.) when extremely well-leveled, bright acid copper deposits are desired.

The additive of bath composition (C) is preferably Rochelle salts, phenol sulfonic acid, etc. Rochelle salts are preferably used in amounts of 10-20 g./l., usually about 15 g./l. The deposition of the first layer of copper plate using bath composition (A) may be carried out by electroplating for 8-18 minutes, say 10 minutes at 60 C.-70 C., say 65 C., using a cathode current density of 3-6 a.s.d., say 4.5 a.s.d. Preferably the bath may be agitated as by air agitation or cathode rocker. During this time copper may be deposited having a thickness of 5.0- 50 microns, typically 15-25 microns, and preferably about 20 microns.

Electroplating the first layer of copper plate from an acid copper plating bath may be carried out at 40 C.- 50" 0., say 45 C., for 35-35 minutes or more, say 25 minutes with vigorous air agitation, at a cathode current TABLE II Minimum Maximum Preferred Component:

Cu 20 30 25 P 140 210 175 Electrodeposition of the first layer of copper from a pyrophosphate-copper bath may be carried out at temperatures of 40 C.60 C., say 50 C. at 35-35 minutes or more, my 25 minutes with vigorous air agitation at cathode current density of 1-4 a.s.d., say 3 a.s.d.

The basis material, typically either (a) a zinc-base diecasting bearing the hereinbefore disclosed first layer of copper plate or (b) the steel basis metal which may bear a first layer of copper plate, may then be further treated in accordance with the process of this invention. Preferably there may be deposited upon the basis material, including the zinc-base die-casting bearing the first layer of copper plate, a second thin layer of cobalt plate having a thickness of 0.255.0 microns (preferably l.32.8 microns). The second thin layer of bright cobalt plate may typically be deposited by electrodeposition from a cobalt electroplating bath having the compositions set forth in Table III or by other means including decomposition of cobalt carbonyl with resultant deposition of a thin bright cobalt layer, or by other means for producing thin cobaltclad base metal.

Typical bright cobalt baths which may be used in prac tice of this invention may include the following components in aqueous solution, all values being in grams per liter (g/1.) unless otherwise indicated:

TABLE III A. Suliamate Bath Component Minimum Maximum Preferred Co (as C0(O3SNH2)Z CoClg' 6H2 C0804, or combinations thereof) 200 400 300 3 3 25 65 45 Saecharin 1. 0 5. 0 3. 2 Sodium allyl suglfloriatth i 1. 4 5 2. 3 Bis-B-hydroxyc y e er 0 2-butyne-1,4-diol 0. 001 0. 5 0. 05 Sodium di-n-hexyl sucelnate. O. 05 0. 5 0. 125 pH (elcctrometrie) 2. 5 4 5 3. 8

B. Fluoborate Bath Co B F 200 500 300 11133033 so 50 45 HBF4 30 50 45 pH (electrometrie) 2 6 3 C. Pyrophosphate Bath Potassium pyrophosphate (hydrated) 50 100 60 Cobalt sulfate, hydrated. 60 150 90 Citric acid. 10 15 Cobalt chloride 50 D. All Chloride Bath CoClg-BHzO 200 500 30 H B O 30 50 E. Mixed Salt Bath Cobalt sulfate, hydrated 200 350 300 Cobalt chloride, hydrated 30 60 .50 Boric acid 30 40 35 Electrodeposition of the second thin layer of bright ductile cobalt plate may be carried out from the plating baths of Table II, by use of a cathode current density of 1-10 a.s.d., say 5 a.s.d., at temperatures of C.60 C., say C. for 2.0 -10 minutes, typically 5 minutes. During this time, a second thin deposit of bright cobalt on the first basis layer of copper metal deposit will form and has a typical thickness of 0.255.0 microns, usually 1.3-2.8 microns, and most preferably about 2.5 microns.

Bath compatible cooperating additives may be incorporated into the cobalt bath compositions of the invention herein. Such cooperating additives may be aromatic sulfonates, sulfonamides or sulfonimides (such as sodium benzene sulfonate, saccharin, dibenzene sulfonimide, etc.); aliphatic or aromatic-aliphatic unsaturated sulfonates (such as sodium allyl sulfonate, sodium-3-chloro-2-butenel-sulfonate, sodium beta-styrene sulfonate, etc.); acetylenically unsaturated compounds (such as 2 butyne1,4-diol and its di-, tetra-, and hexa-substituted ethylene oxide adducts; 2 methyl-3-butyn-2-ol and its ethylene oxide adducts; N-heterocyclics such as N-1,2-dichloropropenyl pyridinium chloride, N-allyl quinaldinium bromide; 2,4,6 trimethyl N-propargyl pyridinium bromide; anionic antipitting surfactants such as sodium lauryl sulfate, sodium di-n-hexyl sulfosuccinate, sodium-Z-ethyl-hexyl sulfate; active sulfur-introducing compounds such as aromatic sulfinates (such as sodium benzene monosulfinate), bisomega sulfopropyl sulfide (sodium salt), etc.

In accordance with the process of this invention a third thin nickel-containing layer is electrodeposited onto the second ductile thin layer of bright cobalt plate. The third thin nickel-containing layer may have a thickness of approximately 2-12 microns. Typically, the thickness of the third thin layer of nickel plate is 3.08.0 microns, usually 4.0-7.0 microns, and preferably about 5 microns.

In accordance with the process of this invention, there is deposited on the second layer of cobalt a third nickelcontaining plate which may be a nickel-containing matrix electroplate or a nickel-cobalt alloy electroplate. Electrodeposition of the nickel may be carried out from plating baths containing nickel sulfate; a chloride, typically nickel chloride; a buffering agent, typically boric acid; and a wetting agent. Other baths may contain, as the source of nickel, a combination of nickel fiuoborate with nickel sulfate and nickel chloride, or with combinations of nickel sulfamate and nickel chloride. Typical Watts-type baths and high chloride baths are noted in Tables IV and V.

TABLE IV \\'ntts-Type Baths Minimum Maximum Preferred Component:

Nickel sulfate 200 400 300 Nickel chloride 30 60 30 50 40 38 65 50 t Mechanical and/or air or solution pumping, etc. pH 5 4. 5 3. 5

TABLE V High Chloride Baths Minimum Maximum Preferred Component:

Nickel chloride 150 300 225 Nickel sulfate- 40 150 Boric acid 30 50 40 Temperature, C 38 65 55 Agitation Mechanical and/or air or solution pumping pH 4. 5 3. 5

There may also be present in the electroplating bath of Tables IV and V primary nickel brighteners in amount of 0.002-0.2 g./l., say 0.05 g./l.; secondary brighteners in amounts of 1-30 g./ 1., say 5 g./l.; and secondary auxiliary brighteners in amounts of 0.5-3 g./ 1., say 1 g./ 1. Typical prima'ry brighteners may include acetylenic compounds such as 2-butyne-1,4diol or pyridinium compounds such as quaternized pyridine derivatives.

Typical secondary brighteners may include, e.g. sulfooxygen compounds typified by saccharin, sodium benzene sulfonate, etc. Typical secondary auxiliary brighteners may include sodium allyl sulfonate.

Deposition of the third layer of nickel containing electroplate may be carried out at 40 C.-60 C., say 50 C. at pH of 2.5-4.5, say 3.5 for 8-14 minutes, say 10 minutes to permit attainment of a nickel-containing plate having a thickness of 2-12 microns, say 5 microns. Nickel alloys such as nickel-cobalt alloy may also be used as the third layer. Bright and semi-bright nickel plate may be used or the third nickel-containing layer may be prepared using a semi-bright nickel layer and a bright nickel coating wherein the total thickness of the nickel-containing layer is about 3-6 microns. Bright nickel and nickel-matrix are preferred as the third nickel-containing layer.

Basis metal bearing these three layers of plate may be useful where a bright nickel plate finish is desired. Other bright decorative nickel finishes may be employed including those identified as satin or brushed finishes, whether produced by mechanical or other means.

When the third thin layer is a nickel-containing matrix, the third thin nickel layer is preferably prepared by a two-step process which comprises affixing to a basis material bearing a conductive material surface of cobalt having a thickness of about 0.255.0 microns a stratum o-f particles having a particle size of about 0.05-5.0 microns and a density on said cobalt metal surface of about 100-5,000,- 000 particles/0111. and depositing in said stratum of particles a conductive nickel-containing layer having an effective thickness of 0.25-5.0 microns which is less than the maximum thickness of said stratum of particles thereby forming a nickel-containing matrix wherein said particles are retained aflixed to said surface in fixed position in said conductive nickel-containing layer, and at least some of said particles intercept the surface of said conductive nickel-containing layer. Typical electroplating baths and processes for preparing nickel-containing matrix layers are described in co-pending patent application Ser. No. 767,- 972, the disclosure of which is incorporated herein by reference.

A typical bath which may be used in practice of this invention may include baths described in Tables IV and V as Well as baths containing the following components as set forth in Tables VI-X, all values being in grams per liter g./ 1.), except as indicated otherwise.

A typical sulfamate-type bath which may be used in practice of the process of this invention may include the following components in aqueous solution (g./l. unless indicated otherwise) A typical chloride-free, sulfate-type bath which may be used in practice of the process of this invention may include the following components in aqueous solution:

TABLE VII Minimmn Maximum Preferred Component:

Nickel sulfate, hydrated. 300 500 405 Boric acid 35 55 40 pH 3 5 4.

A typical chloride-free, sulfarnate-type bath which may be used in practice of the process of this invention may include the following components in aqueous solution:

TABLE VIII Minimum Maximum Preferred Component:

Nickel suliamate. 300 400 350 Boiic acid 35 55 45 pH 3 4. 0

A typical pyrophosphate-type bath which may be used in practice of the process of this invention may include the following components in aqueous solution:

A typical fiuorborate-type bath which may be used in the practice of the process of this invention may include the following components in aqueous solution:

7 7 TABLE X" Minimum Maximum Preferred Component:

Nickel fiuoborate,

hydrated 250 400 300 Nickel chloride, hydratctL 15 60 3O Boric acid 15 30 20 pH 2 4 3. 0

A typical nickel-cobalt alloy bath includes the following components (g. /l.) in aqueous solution:

Minimum Maximum Preferred Component:

NiSO-i-7H2O 200 400 300 COS04-7H20.-.. 15 225 NiCl2-6H2 15 75 60 HaBOa 3O 50 45 It will be apparent that the above baths may contain components in amounts falling outside the preferred minima and maxima set forth, but that most satisfactory and economical operation may normally be effected when the components are present in the ba htsin the amounts indicated.

When the third thin layer containing nickel is a nickelcobalt alloy plate (typically containing about 25-30 percent by Weight of cobalt), a third nickel-containing layer may be deposited from a common bath containing both nickel and cobalt ions by adjusting the current and additive system to permit plating a layer of cobalt followed by a layer of nickel-cobalt alloy in sequence from the same bath according to the invention herein.

When the third thin layer is semi-bright nickel, an aliphatic aldehyde is usually employed in combination with a wetting agent such as sodium di-n-hexyl sulfosuccinate using 200-400 g./l. of NlSO4.7H2O.

Thus, the plating baths may contain bath-compatible brighteners or other bath-compatible additives such as sodium saccharate, wetting agents, etc. High-foaming Wetting agents such as sodium lauryl sulfate may be particularly useful when employed in conjunction with mechanical agitations; and low-foaming agents such as sodium dialkysulfosuccinates may be particularly useful when employed in conjunction with air agitation.

In practice of a preferred aspect of this invention, the basis material bears a first plate of copper, a second thin layer of cobalt (preferably having a thickness of 0.25-5.0 microns) which may be further treated by aflixing thereto a stratum of particles having a particle size of about 0.05- 6.0 microns; deposited thereon a third thin layer containing nickel to form a nickel matrix having a thickness of 2-12 microns and having a sulfur content of less than 0.1% by weight; and a fourth layer of bright decorative chromium. The use of a matrix permits lower effective thicknesses when compared with nickel or nickel-cobalt alloys. Microscopic inspection of the matrix deposit shows that the particles may be retained in fixed position in a matrix of the third thin nickel-containing layer. It will also be observed (as by dark field illumination in a microscope or by the Dubpernell test) that the particles may traverse the nickel-containing layer and may be observed above the upper surfaces thereof.

The composite product so-prepared may typically thus include a first copper metal plate; a second cobalt layer (preferably having a thickness of 0.25-5.0 microns); and deposited thereon a third thin nickel-containing surface having a thickness of 2-12 microns and preferably characterized by having a sulfur content of less than about 0.1% by weight based upon the weight of the nickel-containing layer which is prepared by afiixing to the second thin layer of bright cobalt 100-5,000,000 particles/cmF, each particle having a size of about 0.05-60 microns, said particles being fixed in a thin nickel-containing matrix wherein at least some of said particles traverse said nickelcontaining matrix and intercept the surface thereof.

The nickel matrix layer is prepared by dipping the cobalt-plated article (bearing a thin layer of bright cobalt) into a dispersion bath containing suspended particles having a particle size of about 0.055.0 microns. The bright cobalt-plated article may be maintained in this dispersion for a time (usually for about 30 seconds) sufficient to form thereon a stratum of particles, removed, and then passed to a matrix bath wherein a conductive layer of bright nickel plate is deposited thereon. The nickel plating bath (treated from time to time with active carbon and filtered to maintain the solution free of impurities and insolubles) contains 300 g. of nickel sulfate heptahydrate, 60 g. of nickel chloride hexahydrate, 45 g. of boric acid, and water to make up to one liter at a pH of 4.0 (electrometric). The dispersed material which may be used to prepare the nickel matrix include a wide variety of particles including the following specific materials, such as talc; kaolin; wax; graphite; sulfides such as molybdenum disulfide and tungsten disulfide; pigments including barytes, chromium-cobalt green and cobalt-aluminum blue, and oxides such as silica and alumina; particles of plastic e.g. polymers or copolymers of styrene, butadiene, acrylonitrile, vinyl acetate, vinyl chloride, etc.; diatomaceous earths, powdered aluminum, activated carbon, silicates e.g. sodium silicate; carbonates, e.g. calcium carbonate; carbides; sulfur; etc. including mixtures of these materials.

There may also be present other additives such as polar organic compounds, e.g. amides, amines, long-chain alcohols, acetylenics, etc., to enhance the properties of adhesion, inhibition, or dispersion.

Application of particles may be effected by contacting the basis material with particles. The particles may be blown over the surface of the conductive metal surface of the basis material. The basis material may be dipped into a bed, preferably a fluidized bed of particles i.e. particles suspended in an upfiowing stream of gas. Affixing of particles may be effected by electrostatic or electrophoretic techniques on the basis metal piece. If de- 8 sired, the basis metal may be wet to assist deposition thereon and adherence thereto of the particles.

The preferred particles may be used in the form of a bath i.e. a suspension, emulsion, dispersion, or latex 0f the solid or semi-solid particles in a fluid, preferably a liquid. In one preferred embodiment, the particles may be particles of solid suspended in a liquid in concentration as low as 0.001%, typically 0.l%2%, and preferably about 0.5%. Outstanding results may be obtained by use of baths containing 0.1%2% particles.

Typically the particles in the bath may be from commercially available materials: for example, talc may be obtained having particles ranging in size up to about 7 microns. 0.01%2% of talc may be added to water and dispersed as by milling in a ball mill or in a vVaring Blendor or by stirring. Similar techniques may be employed to disperse wax, pigments, kaolin, etc.

The fluid, typically aqueous medium, in which the particles may be suspended may be water, but preferably is a bath having a composition substantially similar to the bath immediately preceding from which the basis material may have been removed after treatment, e.g. a waterrinse bath or a nickel-plating bath.

Typical particles may be applied from a bath in the form of a dispersion of 0005-5 (preferably 0.5) parts of talc; 95-100 (preferably about 100) parts by weight of water; 0.000050.10 (preferably about 0.01) parts by weight of dimethyl oleamide; and 000005-010 (preferably about 0.01) parts by weight of sodium lignosulfonate.

Application of the particles onto the thin cobalt surface may preferably be effected by dipping the metal surface in an aqueous bath containing said particles. Dipping may be effected at ambient temperature of about -40 C., and the surface may be retained therein for time sufiicient to inundate the surface, typically 5-60 seconds, preferably about seconds. Moderate agitation in this step is advantageous.

The surface may then be removed from the bath bearing a stratum of particles which cling evenly distributed thereon, typically with 100-5,000,000 particles on each square centimeter of surface, and commonly 5,000- 2,000,000 particles/0111. The surface so attained may, if desired, be allowed to dry, or it may be water-rinsed, or it may be further processed immediately (while still hearing a thin film of adherent liquor). The subsequent nickel layer is deposited from a nickel bath which is essentially free of said particles to form a conductive nickel layer which is enmeshed with the adherent particles to form a nickel matrix.

The following examples illustrate typical particulate materials which may be used in the indicated concentrations (expressed as percent by weight, percent w./w.).

Nominal Dispersion Percent particle number Type of dispersed material (W./w.) Designation of dispersed material and supplier size (microns) Latex-polyvinyl chloride 0.5 Dow 700; Dow Chemical Co t), Latex-polyvinyl acetate 0. 027 Plyamul -370; Reichhold Chemical Iuc 0. 5-2.0 .-do- 0. Gelva TS-30; Shawingan Plastics Corp 0. 5 d0. 0.55 do 0.5 Latcx-styrene/butadiene. 0. 024 Firestone PL-SO; Firestone Plastics C0 0. 2 Mos; powder 1.0 Consolidated Astronautics, Inc. 1 WS; powder 1.0 Submicron W52; Bemol, Inc. 0. 4 do 1.0 do.. 0.4 Talc 0.8 Mistron 280; Sierra Talc & Chemical Co. I 0. 4-6 do 0.8 .do 0.4-6 .d0.. 0.8 .(10 0.46 12 Graphite 1.0 Aquadag; Acheson Colloids Company. 1 4. 2 13 do. 0.1 Number 5530; Asbury Graphite Mills, In 2-5 do 0.4 do 2-5 do 1.6 ....do 2-5 Chromium-cobalt pigment. 1.0 V-7687; Ferro Corpl 0. 5 Cobalt-aluminum pigment 1.0 V-3285', Ferro Corp l O. 5 WSz powder plus Cr-Co pigment 1.0 Submieron W82 and V-7687; Bemol, Inc. and Form Corp Talc 0. l5 Misti-on Monomix; Sierra Talc dz Chemical, Inc 1. O-6 0.15 ..d0 1.0-6 0.15 ..do- 1.0-6 0.4 o 1.0-6 0.2 Camel-White; Harry T. Campbell Sons Co 1O Colloidal sulfur 0. O3 Prepared by pouring hot, saturated alcohol solution of sulfur into Wat Maximum. 0.4 (W82) and 0.5 maximum (Cr-Co).

In each of the dispersions described above, either water or the nickel or cobalt electrolyte may be used to form the dispersion dip. In each case, the bright cobalt article containing the adherent particles is subsequently given a thin layer of nickel from one or more of the nickelcontaining baths described herein, and such nickel-containing baths are maintained substantially free of the particles which are present in the dispersion dip compositions which are used.

The tri-layered metal plated composite containing a thin layer of nickel matrix plate having a thickness of 2-12 microns as hereinabove set forth, may then be further plated with a decorative chromium metal deposit. Chromium plating may be effected at temperature of 30 C.-60 C., say 43 C., and current density of 5-50 a.s.di', 'say a.s.d., for'0.5l5 minutes, "say 5 minutes, from a bath containing l00-500 g./l., say 250 g./l. of chromic acid and 1-5 g./l., say 2.5 g./l. of sulfate ion, typically derived from sodium sulfate. Other components including other chromium plating catalysts, e.g. fluoride, silicofluoride or other complex fluorides, self-regulating strontium ion-containing compositions, fume suppressants, etc. may be present in the chromium plating bath.

The chromium plate prepared by the process of this invention may be obtained in thickness of at least about 0.02 microns, typically in decorative thickness of less than about 1 micron, and may be further particularly characterized by its bright decorative appearance, its high corrosion-resistance, and by its microcracked and microporous structure. The chromium plate, which is preferably deposited over the thin nickel matrix plate containing particles which may partially protrude above or intercept the surface of the nickel-containing matrix layer, may possess microcracking and microporosity over substantially the entire area of its surface.

The microcracked surface area of the chromium plate prepared by the process of this invention utilizing the matrix described herein may be found to have at least 100 microcracks per linear centimeter at 40 mm. from the high current density end of a standard Hull Cell panel plated with 10 amperes for 5 minutes at 43 C., compared to 5-10 microcracks per inch for the same chromium on the typical prior art nickel plate. This unexpectedly high degree of microcracking is sufiicient to obtain microcracked areas over all thicknesses of chromium plated in the high and intermediate current density areas. The high degree of microcracking extends sufficiently over the surface of the chromium plate so as to be essentially contiguous with the microporous areas which are characteristic of the low current density areas of the chromium plate on the matrix surface.

This product may be inspected under a microscope and found to contain a microporous surface in the low current density areas of the standard Hull Cell panel. Typically, it may possess a plurality of pores, typically about one hundred to two or three million (at a chromium thickness of less than about 0.5 micron), more or less uniformly distributed over the surface of the metal. Chromium deposited on the third thin layer of nickel plate, prepared by the process of this invention may, thus, be found to contain microporous areas and microcracked areas over the entire surface. It is believed that the presence, over all areas of the chromium plate, of microperforated areas (i.e. either microporous areas or microcracked areas), in conjunction with the Cu-Co-Ni composite described herein makes it possible to attain the novel benefits herein set forth.

When chromium plating is applied to the copper-cobaltnickel matrix-stratum described herein unexpected benefits are derived. Other factors being constant, the cracking of a chromium plate will depend on its thickness. Such factors as concentration of chromic acid, concentration of catalyst materials, temperature of plating, etc.; all have an effect. It is characteristic of prior art chromium deposits generally that no cracking appears throughout 10 the first stage of deposition, up to about 0.5 micron. As the thickness is increased in the undesirable second stage, e.g., in the range of 0.51.0 microns, gross cracking may develop; in the undesirable third stage, e.g., about 1.0- 1.5 microns, spangle-type cracking, i.e., microcracking interspersed in gross cracking, may develop. In the fourth stage, microcracking alone may develop. The undesirable intermediate stages, i.e., stages two and three, may be objectionable in appearance in the as-plated condition and particularly so after the initiation of corrosion has emphasized the presence of the cracks. Micropores and microcracks are not objectionable because the fineness of structure is not perceived by the eye except with aid of magnification. Furthermore the presence of these microperforations over the entire plate, permits attainment of the outstanding corrosion-resistant properties hereinafter set forth.

It has been unexpectedly found in the practice of this invention that microporosity is produced in stage one and microcracking is facilitated so that the undesirable stages two and three, i.e., gross and Spangled-type cracking, do not appear. Thus, a final plated chromium part may have microporosity where low current densities occur and microcracking in higher current density areas with no objectionable gross cracking or spangle.

The preferred thickness of the bright decorative electroplated chromium plate may be 0.02-5.0 microns, say 0.5 microns. The degree of microcracking (attained at thickness greater than about 0.5 micron) over a typical coppercobalt matrix nickel plate may be at least microcracks per linear centimeter.

In the following series of examples, unless otherwise specifically noted, basis metal panels were plated with a bright copper plate in a standard bright copper plating bath. The bright copper plated panel was water rinsed, given a layer of 0.25-6 microns of bright cobalt (as shown in Tables XI and XII) and then (where indicated) the panels were dipped into a dispersion bath containing the suspended particles as designated in Table XH. The metal panel bearing the thin layer of cobalt plate was maintained in this bath for about 30 seconds to form thereon a stratum of particles, removed, and passed to a matrix bath wherein a conductive third layer of nickelcontaining plate was deposited thereon. The nickel-containing plating bath (treated from time to time with active carbon and filtered to maintain the solution free of impurities and insolubles) contained 300 g. of nickel sulfate heptahydrate, 60 g. of nickel chloride hexahydrate, 45 g. of boric acid, and water to make up to one liter at a pH of 4.0. Table XI indicates those examples which employ a nickel-containing electroplate which is not a particlecontaining nickel matrix. Table XII includes examples which employ a nickel matrix.

After deposition of the nickel-containing layer, the panel was rinsed with water, and then chromium plated in a bath containing 250 g./l. of chromic acid, 2.5 g./l. of sulfate (added as sodium sulfate) at 43 C.

In Tables XI, XII, XIII, and XIV the CASS rating is given as a pair of numbers wherein the first number indicates the degree of basis metal corrosion and the second number indicates the appearance. In each case, over a scale of 0 to 10, the higher numbers indicate a better rating; and values greater than 7-8 are acceptable.

Each example used steel panels which were run in duplicate. All panels were given a final layer of 0.25 micron of chromium prior to testing for the CASS rating.

As can be readily seen from Table XI, in Examples 3 and 4 wherein a layer of 6 microns of nickel was used in place of the layer of 1 micron of cobalt followed by microns of nickel (as in Examples 1 and 2 which illustrate the invention herein), the CASS ratings were completely unsatisfactory (O/O) both at 22 hours and 44 hours. In Examples 7 and 8, the first layer of copper was omitted and as can be seen from Table XI, the CASS ratings at 22 hours were much poorer than the ratings obtained in Examples 1 and 2. At 44 hours, the CASS ratings for Examples 7 and 8 were completely unsatisfactory.

In the following examples, a nickel-containing matrix was used as the nickel-containing layer using talc particles (0.1% talc-Mistron Monomix in water). A final layer of 0.127 microns of chromium was used prior to l Bright nickel.

As can be seen from Table XII, less nickel thickness is used when a nickel matrix is employed and the total thickness of the cobalt-nickel layer of the composite of the invention may be reduced while still obtaining outstanding CASS ratings.

In control Example 9, a 7.6 micron layer of bright nickel was used in place of the cobalt-nickel matrix layers and the resulting CASS ratings were lower both for 22 hours and for 44 hours.

In the following, examples, comparisons were made to show the efiects of the substitution of a first layer of nickel (from two different nickel plating baths) in place of the first layer of copper as employed in the invention herein.

The aqueous bright copper bath used was the same as employed in- Example 1 and contained 240 g./l. CUSO4'5H2O; 60 g./l. H 50 0.06 g./1. chloride ion; 1.0 g./l. polyether; and about 0.02 g./l. of sulfonated disulfide The second aqueous nickel plating bath used in the following Table XIII (designated Bright Nickel Bath II) contained 300 g./l. NiSO -7I-I O; 60 g./l. NiCl -6H O; 35 g./l. H BO 0.02 g./l. primary brightener (mainly acetylenic diol) and 0.125 g./l. wetting agent (sodium di-n-hexyl sulfosuccinate).

The aqueous bright cobalt bath used to prepare the bright cobalt layer of Table XIII was composed of 300 5.0 g./l. saccharin; primary brightener (mainly butyne diol); and wetting agent (sodium di-n-hexyl sulfosuccinate).

Identical steel panels were given layers of electroplate using the foregoing baths and the final 0.25 micron thick chromium layer was electrodeposited using the chromium plating bath of Example 1 with the same plating conditions. The results are'summarized in Table XIII.

TABLE XIII Thickness (microns) of electroplated layer CASS rating As can be seen from Table XIII, the use of a first layer of nickel having the same thickness as the first layer of bright copper results in CASS ratings which are lower at 44 hours.

In the following examples (summarized in Table XIV) steel panels identical to those employed in the experiments of Tables XI-XIII were used. The first layer of copper was deposited from an aqueous bright copper bath as described for Table XIII using the identical plating conditions to deposit the same thickness of copper. The second layer of cobalt was similarly deposited over the first layer of copper from an aqueous bright cobalt bath as described for Table XIII using identical plating conditions to produce' a second bright cobalt electroplate having a thickness of 2.5 microns as shown in Table XIV.

A third nickel-containing layer having the thickness described in Table XIV was prepared using a nickelcobalt which contained 240 g./l. NiSO 60 g./l. CoSO -7H O; 60 g./l. NiCl -6H O; 45 g./l. H BO and alloy anodes composed of 80 percent by weight of nickel and 20 percent by weight of cobalt.

The 0.25 micron thick chromium layer was applied in the same manner from an identical bath as described for Example 1.

The control (Example 18) was identical in all respects to Example 17 except that a layer of semi-bright nickel 3 microns thick was employed in place of the 2.5 micron layer of bright cobalt (layer II) in Example 17. The semibright nickel layer was prepared using a bath as described in USP 3,486,989 containing 300 g./l. NiSO -7H O; 45 g./l. NiCl -6H O; 45 g./l. H BO and 0.15 g./l. piperonal using an electrometric pH of 3.8;4.0. The results are summarized in Table XIV.

TABLE XIV Thickness (microns) of electroplated layer III-Bright CASS rating nickel cobalt Example No. I-First layer II-Second layer alloy 22 hrs. 44 hrs.

17 18 (Bright copper) 2.5 (Bright cobalt) 1.8 10/10 10/9 18 (control) d0 3.0 (Semi-bright nickel)... 1.8 10/9 10/6 The first aqueous nickel plating bath used in the following Table XIII (designated Bright Nickel Bath I) contained 300 g./l. NiS0 -7H O; g./l. NiCl -6H O; 35 g./l. H BO 0.05 g./l. primary brighteners (mainly butyne diol); 5.0 g./l. secondary brightener (saccharin); and 0.125 g./l. wetting agent (sodium di-n-hexyl sulfosuccinate).

As can be seen from Table XIV, the CASS ratings for Example 17 (illustrating the invention) were superior to the ratings obtained using the control at both 22 hours and 44 hours.

It is believed that the improved properties obtained (especially improved corrosion resistance) according to the invention herein is due to the maintenance of proper balance between the electrochemical activities in the various layers of the composite. It is believed that since cobalt corrodes more readily than either nickel or copper, sacrificial corrosion of the cobalt layer occurs when the corrosion path reaches said cobalt layer. Apparently the activity of the cobalt layer is not quite as sensitive to sulfur content as is a nickel layer, and, therefore, the cobalt layer tends to corrode preferentially. The relative activities of the metal layers of the composite can be obtained by measuring the potentials of these metals against the standard calomel electrode in air-saturated 3% by Weight aqueous sodium chloride solution. It has been found that the incorporation of cobalt into a bright sulfur-containing nickel deposit up to a weight percent of about 50 has only a slight effect on this potentiaLHowever, as the cobalt content increases beyond the 50% by weight value, the potential changes more rapidly in the more active direction. On the basis of this information, it is believed that cobalt protects the nickel and chromium in a manner similar to the protective action provided by zinc for steel in galvanized iron. This hypothesis appears to be borne out by cross-sectional photomicrographs of corroded deposits which show that corrosion pits extending to the cobalt layer also extend laterally to preferentially corrode the cobalt layer, whereas the copper layer appears to be relatively intact. Thus, it is especially surprising that extremely thin cobalt layers could be used at all to produce superior effective corro sion improvement. It is believed that the thin layers of cobalt become effective because the resistance of the path of electrical current is increased by its relatively small physical dimensions and that the corrosion current between the oobalt and the chromium is thereby decreased, although such current is still sufficiently large to prevent nickel corrosion.

Although this invention has been illustrated by reference to specific examples, numerous changes and modifications thereof which clearly fall within the scope of the invention will be apparent to those skilled in the art.

I claim:

1. The process for preparing a bright decorative chromium composite metal coating which comprises:

(1) depositing on a basis metal a first layer of copper plate;

(2) depositing on said copper plate a second thin layer of cobalt;

(3) depositing on said layer of cobalt a third thin layer containing nickel having a thickness of 2-12 microns; and

(4) electrodepositing on said third nickel-containing layer a fourth layer of bright decorative chromium.

2. The process as claimed in claim 1 wherein the second thin layer of cobalt has a thickness of 0.255.0 microns.

3. The process as claimed in claim 1 wherein the third thin layer containing nickel has a sulfur content of less than 0.1 percent by weight.

4. The process as claimed in claim 3 wherein the third thin layer containing nickel is prepared by afiixing to the second thin layer of cobalt a stratum of particles having a particle size of about 0.05-15 microns and a. density on said thin layer of cobalt of about 1005,000,- 000 particles/cm. and depositing in said stratum of particles a conductive thin nickel-containing layer having an effective thickness of .25-5.0 microns which is less than the maximum thickness of said stratum of particles thereby forming a matrix wherein said particles are retained aflixed to said cobalt surface in fixed position in said conductive thin nickel-containing layer, and at least some of said particles intercept the surface of said conductive thin nickel-containing layer.

5. The process as claimed in claim 4 wherein the density of said particles on said thin layer of cobalt is 5,0002,000,000 particles/cmP.

6. The process for preparing a bright decorative chromium composite metal coating which comprises:

(1) depositing on a basis metal a first layer of copper plate having a thickness of 5.0-50 microns;

(2) depositing on said copper plate a second thin layer of cobalt having a thickness of 025-50 microns;

(3) aflixing to said thin layer of cobalt a stratum of particles having a particle size of about 0.056.0 microns and a density on said thin layer of cobalt of about 5,000,000 particles/cmP;

(4) depositing in said stratum of particles a conductive nickel metal layer having an effective thickness of 0.25-5.0 microns which is less than the maximum thickness of said stratum of particles to form a third thin layer of nickel-containing matrix having a thickness of 025-60 microns; and

(5) electrodeposition on said third thin layer of nickelcontaining matrix a fourth layer of bright decorative chromium.

7. The process of claim 6 wherein the fourth layer of bright decorative chromium has a thickness of at least 0.02 micron.

8. An article bearing a bright decorative chromium composite metal coating wherein sai dcoating comprises:

(1) a first layer of copper;

(2) a second thin layer of cobalt thereon;

(3) a third thin layer containing nickel having a thickness of 2-12 microns; and

(4) a fourth layer of bright decorative chromium electrodeposited on said third nickel-containing layer.

9. An article as claimed in claim 8 wherein the third thin layer containing nickel has a sulfur content of less than 0.1 percent by weight.

10. The article as claimed in claim 9 wherein the second and third layers each have a thickness of 025-50 InlCI'OIlS.

11. The article as claimed in claim 9 wherein the third thin layer is ia nickel matrix.

12. The article as claimed in claim 9 wherein the third thin layer comprises a nickel matrix containing latex plastic particles having a particle size of about 0.056.0 microns and a density on the second thin layer of cobalt of 1005,000,000 particles/cmF.

References Cited UNITED STATES PATENTS 3,428,441 2/1969 DuRose 29196.6 X 3,449,223 6/1969 Odekerken 29196.6 X 3,471,271 10/1969 Brown 29-19615 X OTHER REFERENCES Nathaniel Hall, How About Cobalt?, Metal Finishing, November 1969, p. 43.

L. DEWAYNE RUTLEDGE, Primary Examiner J. E. LEGRU, Assistant Examiner US. Cl. X.R.

Notice of Adverse Decision in Interference In Interference No. 98,440 involving Patent No. 3,679,381, H. Chessin, NOVEL COMPOSITE, final judgment adverse to the patentee Was rendered May 1, 19%, as to claims 1, 2, 3, 8, 9, 10 and 11.

[Ofiiczal Gazette of September 24,1974] Disclaimer 3,67 9,381.Hyman C'hessz'n, Birmingham, Mich. NOVEL COMPOSITE. Patent dated July 25, 1972. Disclaimer filed July 26, 1974, by the assignee, M cf: T Chemicals, Inc; Hereby enters this disclaimer to claims 1, 2, 3, 8, 9, 10 and 11 of said patent.

[Ofiicz'al Gazette illarch 1], 1975.]

Notice of Adverse Decision in Interference In Interference No. 98,440 involving Patent No. 3,679,381, H. Chessin,

NOVEL COMPOSITE, final judgment adverse to the patentee was rendered May 1, 1974, as to claims 1, 2, 3, 8, 9, 10 and 11.

[Oyfieial Gazette of September 24,1974] 

